Television receiver



May 12, 1942. H. R. LUBCKE TELEVISION RECEIVER Filed Nov. 25. 1939 Inventor, flarry J? Lube/2e, f

Attorney frequ enqy Patented May 12, 1942 UNITED STATES PATENT OFFICE 2,282,487 TELEVISION RECEIVER Application November 25, 1939, Serial No. 306,084

7 Claims.

My invention relates to radio receiving circuits, and particularly to those which are adapted for ultra-high frequency television reception. It resides chiefiy in methods and means for amplifying intercepted sight and sound modulated carrier energy in a single amplifying channel, and. for separating the sight energy from the sound energy prior to detection.

In the present practice of television, image modulated energy often is sent 'on an ultra-high carrier frequency, such as 45 megacycles with a band width of 2 or 3 megacycles; while the accompanying sound energy is modulated on an ultra-high carrier frequency such as 49.75 megacycles with a band width of only or kilocycles. The television receiver in such cases, is required to amplify both the wide and narrow sideband carriers, and to separate their energies from each other. In the present invention, a special coupled circuit, sharply tuned resonant circuits, and a non-loading detector, are employed to isolate the relatively narrow band of sound energy.

An important object of my invention is to attain simultaneous amplification of both sight and sound energy at carrier frequency; and the separation of these two kinds of energy, after amplification and while still at the original carrier frequency. Another object is to separate the two kinds of carrier energy by means of one broadly tuned, and one sharply tuned group of resonant circuits. A third object is to secure sharp tuning in resonant circuits operating at ultra-high frequencies, by the use of very high impedance detectors. A fourth object is to provide a simple sight-sound television receiver which does not require either a frequency changing oscillator, separate amplification channels for modulated sight and sound energy, nor one more detector than the number of carrier frequencies to be received (as in the known type of superheterodyne television receiver).

Other objects and advantages of the invention will appear in the following description thereof, and will occur to those familiar with the art involved.

My objects have been attained in the manner illustrated in the accompanying drawing, in which- Figure 1 shows a complete schematic diagram of my television receiver;

Figure 2 illustrates a family of resonant circuit response curves; and

Figure 3 shows an alternate arrangement of certain parts of the apparatus shown in Fig. 1.

.. sound.

Referring to the drawing, a dipole receiving antenna is indicated at.5. This is adapted for intercepting electro-magnetic energy which has been modulated for transmitting both sight and. The intercepted energy is conducted through antenna coil 6 to ground, either directly as shown, or through feeders in a manner known to the art. The type of antenna used with my receiver is not of importance, and reflectors may be used if desired.

The first radio frequency coil is indicated in its co-operative position at I. This may well be of the extensible type described in my copending U. S. patent application No. 268,268 for Band pass filter, filed April 1'7, 1939. In such coils, which may be utilized throughout the receiver diagrammed in Fig. 1, the inductance is variable, and associated variable condensers are not required. Hence I have indicated fixed condensers at B, 9, 10, ll, I2 and I3. These are shown as being, and in practice they are, relatively small. They may at times, and preferably, consist largely of the stray capacitances of the circuits to which each of the corresponding impedance coils is connected. Resistor I4 is shown shunting coil 1, for the purpose of broadening the frequency response thereof; and similar resistors may, or may not be utilized across coils IS, IS, II or l8.

Although I prefer the described arrangements, the use of fixed coils with variable condensers, or other tuning means known to the art, also may be employed. By varying the resonant frequency with any of these arrangements, television energy of other frequencies than the 45 and 49.75 megacycles mentioned, may be received.

Vacuum tube l9 is the first radio frequency amplifying means that I employ. It may be of the high mutual conductance type, or of the acorn type. Many of the circuit components which are associated therewith in Fig. 1, are' arranged according to known methods for supplying operating voltages, or for by-passing radio frequency energy. It therefore seems to beunnecessary to reference, or to separately describe them.

In the anode circuit of tube l9, coil l5 and distributed capacitance 9, form the primary of a band pass circuit which is completed by secondary coil l6 and its associated capacitance Ill. The frequency versus response characteristic of this circuit, may have two widely spaced humps, such as those of curve 20 in Fig. 2. This is known to be common in response curves of closely coupled band pass circuits of small resistance. Such a curve complements the response curve of coil 7, capacitance 8, and associated resistor M; the latter curve being high in the center with sloping sides, like that at 2| of Fig. 2. The resultant of these two curves is substantially flat topped, like that at 22 of Fig. 2. In that figure, line 23 denotes the visual carrier frequency, and line 24 denotes the aural carrier frequency, with respect to the response curves. The accepted visual side band extends from line 23 nearly to line 24.

Vacuum tube 25 is the second radio frequency tube. In Fig. 1, two stages of radio frequency amplification are shown, but this may be varied at will. For strong carrier energies, as when the receiver is adjacent to a transmitter, no radio frequency amplification may be required; but, for high sensitivity, several radio frequency stages may be used. In practice, I have found it desirable to vary the gain of the radio frequency amplifier, by means of a variable cathode resistor 26 in the circuit of one of the radio frequency tubes.

Energy for visual purposes is separated in my receiver from other types of transmitter energy, by means of the coils l1 and I8. The latter may be of similar construction to coils 1 and I6. Coil I1 is either a variable or fixed inductance, but of large diameter compared to coil IB. The purpose of this is to secure largely inductive coupling between coils I1 and I 8, and relatively small capacitive coupling. Coil I8 is connected to diode 21, which constitutes a desirable form of visual energy detector. Other known types of detectors may be employed; but, if they do not constitute an appreciable resistance load on coil IS, the latter should be loaded with a resistor of appropriate size. A resistance value of a few thousand ohms should be employed for the purpose, so that this circuit will pass either one or both of the 2 or 3 megacycle image sidebands, without frequency discrimination.

The second electrode of diode 21 is connected to resistor 28, and high frequency response improvement inductance coil 29, according to usual television amplifier practice; and the output from the diode is conducted to a visual amplifier, designated in Fig. 1 at 30.

An advantage of my system of separation and detection at incoming carrier frequency is, that resistor 28 and inductor 29 need not be bypassed by a condenser to remove the radio frequency energy. This is necessary with the superheterodyne type of receiver. In the latter, the radio frequency is heterodyned down in frequency, and must be removed by a condenser having twenty-five micro-microfarads capacitance or more. Such a condenser seriously limits the voltage output that can be obtained from the detector stage while concurrently preserving the uniformity of frequency and phase response which is necessary in television amplification. In my system, the stray circuit capacitances alone, are eifective for by-passing the radio frequency energy.

With a negative image radiated by the television transmitter, visual amplifier 30 should have an even number of stages for the connections of diode 21 shown. The electrodes of diode 21 may be interchanged as to their connections to coil l8 and resistor 28; in which case an odd number of stages may be utilized in amplifier 30 to give the desired positive image on cathode ray tube 3 I. Suitable scanning oscillators, and power supply connections for operating the cathode ray .lished television transmitter.

tube, are known to the art. Therefore it has not been thought necessary to show or describe them here.

The sound carrier energy is separated from the plurality of incoming energies in the chan nel, by coils 32 and 33. It will be noted that coils l1 and 32 are in series in the anode circuit of final radio frequency amplifier vacuum tube 25. Coil 32 comprises only a half turn, and is coupled closely to coil 33 near its grid end. The coupling between coils 32 and 33 therefore is largely capacitative.

Coil 33 is of low loss construction, so as to tune as sharply as possible; and it is tuned to the sound carrier frequency. In practical embodiments of this circuit, coils 1, l5, l6, l1, l8 and 33, have been arranged with a gang adjustment, by means of a single shaft constituting the manual tuning control for the receiver.

Vacuum tube 34 is the aural energy detector of my receiver, and is shown as being of the cathode-output, infinite-impedance type. As such, it imposes a negligible resistance load on coil 33, thereby preserving sharp tuning characteristics. The detected sound output appears across resistor 35, is conveyed to an aural amplifier indicated by rectangle 36, and thence to loudspeaker 31. It is possible to utilize cathode bias triodes, or multi-electrode types of detector tubes, instead of the infinite impedance type circuit elements 34 and 35.

In recapitulation, it is to be noted that the necessary sight-sound energy separation is accomplished in my receiver at original carrier frequency. This is done by employing a visual energy detector, and coils having broad bandpass characteristics, in inductive coupling relation thereto; and by using an aural energy detector having negligible loading characteristics, and fed from a sharply tuned coil which is largely in capacitative coupling to the common input circuit.

It has been found in practice, that coils l5, I6, I! and I8 must be Wound in the same direction when the plate and grid connections are at the opposite ends thereof; or be wound in opposite directions when the plate and grid connections are at the same ends. Such arrangements give maximum gain, with a minimum tendency toward regeneration. Coils 7, I6, 18 and 33, may satisfactorily have seven turns of 1" diameter; and coil I1 may have two turns of 1%" diameter.

I have found in practice, also, that it is important to have a capacitative coupling in the tuned circuit of the aural energy detector; and

that, if this is accomplished, alternative forms of that circuit may be used. Such an alternative is illustrated in the diagram of Fig. 3, and has been operated. In that form I have used only simple conducting elements 38 and 39, in place of the half turn coil 32. Element 39 may be merely the end of conductor 38; or a plate electrode may be employed to increase the capacitance to the grid end of coil 33. In either case, the coupling necessarily is almost wholly capacitative.

The receiver circuits should be housed in shielded compartments, in the manner indicated by dotted lines 40 of Fig. 1.

Several receivers have been constructed according to the foregoing specifications; and these have been operated for considerable periods of time, at distances of many miles from an estab- Observation of the performances of these receivers,,has fully established the several criteria outlined herein.

It will be remembered that, as standardized, aural energy carriers always are higher in frequency than visual energy carriers. The capacitative coupling between coils 32 and 33, or the simple conducting elements 38 and 39 used as alternates for half-turn coil 32, is in the form of a series capacitance of small value. This has a low reactance to the higher aural carrier frequency; allowing greater energy transfer thereat, and less transfer at the lower visual carrier frequency. Such functioning, combined with that of the sharply tuned resonant circuit of the aural carrier, and the non-loading aural detector which makes the arrangement possible, is responsible for the rejection of the visual energy from the aural signal channel. The aural energy is rejected from the visual signal channel, by the lack of response of the visual resonant circuit to aural carrier frequency; and also by the reduced responses at aural carrier frequency of the several resonant circuits for amplifying the radio frequency. The latter functioning is illustrated in Fig. 2, by the fact that line 24 crosses the curves at a considerable distance from the peaks, on the down side.

The required adjustments for accomplishing the performance described, may be made while the receiver is being manufactured; utilizing for the purpose either a sight-sound television signal from an established broadcasting station, or a laboratory replica thereof.

It is possible to employ a stage of strictly visual channel radio frequency amplification, and one of strictly aural channel radio frequency amplification, after securing the results from the separation circuits as they have been described above. This will give even greater separation of the two types of energy. However, such additional amplification has been found not to be necessary in the use of the separation circuits described. The simplification which is the result of omitting such additional amplification is an important feature of the present invention.

Having thus fully disclosed What I have invented, I claim:

1. In apparatus for sight-sound television reception, means for separating sight and sound energy at carrier frequency, comprising a con ductive circuit in which said energy may fiow; the circuit having a predominately inductive coupling between it and a channel for a portion of the separated energy, and a predominately capacitive coupling between it and another channel for another portion of the separated energy.

2. In a sight-sound television receiver, means for separating and demodulating sight and sound modulated radio frequency energy having sight modulated and sound modulated components, comprising; a coil shunted by a diode detector and tuned to accept the sight modulated component of said energy; a second coil which is inductively coupled to the first said coil; a third coil shunted by a non-loading type detector and sharply tuned to accept the sound modulated component of said energy; and a conductor in circuit with the second coil and in capacitative coupling relationship to the third coil; said second coil and said conductor being connected to a circuit of said receiver wherein both said sight and sound modulated radio frequency energy flows.

3. A device for receiving two radio frequency signals of slightly different frequency, comprising; circuits adapted for simultaneously amplifying the two signal energies but affecting the energy of the higher frequency to a lesser degree; a separating circuit composed of a resonant circuit having substantial resistance, inductively coupled to said amplifying circuits for separating the energy of the lower frequency from the common signal; and a separating circuit composed of a resonant circuit having small resistance, capacitatively coupled to said amplifying circuits for separating the energy of the higher frequency from the common signal.

4. In a television receiver for sight-sound television signals comprising a visual modulated and an aural modulated carrier, wherein the aural energy carrier is at the higher frequency; an amplifier for simultaneously amplifying the visual and aural energy carriers; a resonant circuit having substantial resistance, inductively coupled to said amplifier, for separating the visual energy carrier from the common signal; and a resonant circuit having small resistance, capacitatively coupled to said amplifier, for separating the aural energy carrier from the common signal.

5. A sight-sound television receiver comprising; means for intercepting television modulated electrical energy having sight and sound components; means for simultaneously amplifying the sight and sound components of said energy, at the frequencies when intercepted; means for separating said components which include, a coil of relatively large diameter and several turns connected to said amplifying means, a coil of considerably smaller diameter which is tuned to the sight carrier frequency and inductively coupled to the first said coil, a coil of less than one turn connected to said amplifying means, and a low-loss coil which is tuned to the sound carrier frequency and capacitatively coupled to the third said coil; means for demodulating each of said components separately, connected to said smaller diameter coil and said less than one turn coil. respectively; and means for reproducing the en tire televised subject-matter from said demodulated components.

6. A television receiver for accomplishing simultaneous reception of sight and sound modulated carrier frequency energy having sightmodulated and sound-modulated components, comprising; a group of resonant circuits which is responsive to each component of said energy; a thermionic amplifying device which can co-act with each of said circuit groups; a circuit group to separate said components, which includes a resonant circuit tuned for the sight-modulated energy component, a coil having a largely inductive coupling to the last said circuit and connected to said amplifying device of said first group, a resonant circuit sharply tuned for the soundmodulated energy component, and a conductor having a largely capacitative coupling to said sharply tuned circuit and connected to said am plifying device of said first group; means for demodulating and amplifying each of said components separately, connected to said coils tuned to said components respectively; and means for reproducing the entire televised subject-matter from said demodulated and amplified components.

'7. In a sight-sound television receiver for incoming television-modulated composite energy having sight and sound components, co-operative elements comprising; a group of amplifying devices for each stage of incoming carrier frequency amplification; a circuit for separating said sight and sound energy components; a second group of devices constituting an incoming energy channel to said circuit for separating sight signal energy from the composite energy, and including two coils in inductive coupled relation, one of which is connected to said first group and one to said second group; a third group of devices constituting an incoming energy channel to said circuit for separating sound signal 10 energy from the composite energy, and including a sharply tuned coil and an associated capacitance which is resonant to the frequency of the sound component, and a conductor which is in capacitative relation to said sharply tuned coil, said coil being connected to said third group, and said conductor to said first group; each of said groups being housed in an electromagnetic shield compartment.

HARRY R. LUBCKE. 

